1. Field of the Invention
This invention relates to an optical information recording carrier for performing optically recording and/or reproduction of information.
2. Related Background Art
In recent years, with the progress of information growth in society, there have been proposed many information recording carriers and devices for recording and reproducing information as means for handling a diversity of information with good efficiency. Such recording carriers may include those, in which the information is converted to binary values which can be detected by conversion to changes in reflectance, changes in intensity of the reflected light accompanied with the changes in the surface shape such as presence or absence of pit.
Among the recording carriers which depend on a change in optical reflectance, there have been proposed the so called heat mode recording materials, in which recording is effected by irradiating an energy beam such as laser beam in spots onto the recording layer to have a part of the recording layer undergo a change in state.
These recording materials are the so called DRAW (direct read after write) media in which it is not required to perform developing processing after writing of information, but which also afford high density recording as well as additional writing.
Among the recording-reproducing devices for optical informations, are systems in which grooves are pre-formed at certain intervals on the substrate surface thus providing a track servo for writing and reading. According to this system, the grooves play the role of a guide, and therefore track control precision of laser beam can be improved, whereby higher speed access results when compared with systems using grooveless substrate of the prior art.
FIG. 6 is a schematic sectional view of an optical information recording carrier of the closely contacted encapsulation type as described in the prior art. In FIG. 6, 1 is a transparent substrate made of a resin, 2 a track groove portion, 3 an optical recording layer, 4 an adhesive layer and 5 a protective substrate.
In FIG. 6, optical writing and reading are performed for recording and reproduction of information through the transparent substrate 1 and the track groove portion 2. By utilizing the fine unevenness of the track groove corresponding to the guide groove for light, tracking can be performed through the phase difference in the reflected light of the laser beam. Also, the optical information recording carrier of the closely contacted encapsulation type can be easily prepared obtained by forming an optical recording layer 3 on the track groove portion 2 of the transparent substrate 1 and plastering the protective substrate 5 through the adhesive layer thereon.
Such optical information recording carrier of the closely contacted encapsulation type as shown above in FIG. 6, has the drawback that it is generally lower in recording sensitivity as compared with an optical information recording carrier of the hollow structure type having, for example, an air layer (or space layer) provided therein. For example, in the case of the hollow structure type, the recording material constituting the optical recording layer is melted or sublimated by the light.fwdarw.heat conversion by light absorption to form recording pits, resulting in remarkable change in optical characteristics such as transmittance, reflectance, etc. at the recorded portion. In contrast, in the case of the closely contacted encapsulation type, the physical changes as mentioned above, namely the changes in shape such as pit formation, etc. through melting or sublimation are considerably inhibited, and instead thereof, chemical changes, for example, pyrolysis of the recording material constituting the optical recording layer through light.fwdarw.heat conversion by light absorption occurs to form recording pits by decoloration or discoloration, whereby a drawback results in that recording sensitivity is lowered due to change in optical characteristics such as transmittance, reflectance, etc. at the recorded portion.